1. Field of the Disclosure
Friction welding is the process for welding together two bodies or workpieces by converting mechanical energy to heat energy by the friction between the engaging weld surfaces of the two workpieces.
2. Description of the Related Art
In rotary friction welding, the process involves effecting relative rotation between the two workpieces while the weld surfaces remain in engagement with each other. In linear friction welding, the process involves effecting relative lateral oscillation between the two workpieces while the weld surfaces remain in engagement with each other.
For example, in inertia rotary friction welding one of two coaxial workpieces is attached to a flywheel, rotated to a predetermined speed and then driven against the second workpiece using thrust supplied by the welding machine. A fixed amount of stored energy in the flywheel (proportional to rpm2·l, where rpm is the flywheel's predetermined speed and l is its rotational inertia) is thereby converted to heat by friction at the interface of the engaging weld surfaces, which bonds the workpieces together.
The initial contact between the weld surfaces produces a conditioning period in which friction raises the temperature at the interface. This is followed by upsetting when the temperature reaches a high enough level such that softening/melting of the workpiece material allows the workpieces to be pushed together, with liquid or quasi-liquid material being expelled as flash sideways from a plasticised zone at the interface.
A problem can arise, however, that during upsetting the plasticised (liquid or quasi-liquid) material at the interface may not be expelled efficiently as flash, preventing or hindering the removal of interfacial contaminants. As used herein by “flash” we mean not only such expelled material, but also plasticised material at the interface that is desired to be expelled.
A further problem can arise that the distribution of energy input into the weld may not be optimal. For example, in rotary friction welds, the inside diameters of the weld may receive less energy than the outside diameters of the weld due to the differences in relative rotation speed.